1. Field of the Invention
The invention in general relates to the field of implantable connectors for making physical and electrical connection to and between implantable leads, and more particularly, concerns an improved connector that permits a lead and an extension to be joined at any point along their length, and which provides a dynamic gripping action that permits a positive connection without the use of set screws, adhesives, etc.
2. Description of the Prior Art
In recent years, many devices have been developed which are designed for implantation in a body. For example, electrical tissue stimulators are now routinely implanted in humans for treatment of heartblock, pain, scoliosis, and other medical problems. Generally, an electrical lead is used with these devices to carry an electrical current or voltage from a pulse generator or other electrical device to the body part that needs to be treated. Such leads generally consist of a conductor encased in an insulator which is generally inert to body fluids. In many such leads, the conductor is in the form of a coil with a passage down the center of the coil called lumen. The conductor is made in this form because such coil conductors are extremely flexible and highly resistant to breakage; in addition the lumen permits the insertion of a stylet into the lead to stiffen the lead during implantation to allow it to be handled and placed more easily.
As the art of the implantable devices, and the leads for use with the implantable devices has developed, so also has the art of connectors for connections between the implantable devices and the leads developed. Conventional electrical connectors used in external applications generally are not suitable for use with implanted devices. Implanted devices must be highly reliable because the health and life of patients may depend on them for long periods, such as ten years or more, and because they cannot be replaced except by expensive and traumatic surgical procedures. In addition, such devices must be capable of such high reliability in a hostile environment--the human body--in which they are subject to much movement and flexing. For these reasons, up to now, such connectors have consisted of relatively complex positive fixation devices encased in protective materials. Perhaps the most common of such devices has been a pin socket type arrangement containing a set screw in the socket which can be screwed down upon the pin after the pin has been inserted to positively hold the pin in place, with the whole encased in protective medical-grade silicone or similar material. Such connectors tend to be significantly larger than the lead itself and thus add significant bulk to the implantable lead. The larger the implanted device, the more trauma it may cause the body, and thus it is desirable to have smaller connectors. One solution to this problem has been the use of medical adhesive to hold a pin and socket device together. While the use of the medical adhesive may solve some of the bulk problem, it has its own disadvantages, such as difficulty in making a disconnection without destroying the part if a disconnection is necessary, contamination of the site due to particles which become loose, failure of the adhesive under flexing, etc.
Conventional implantable electrical connectors have, up to now, required special fittings on the lead or other terminal which it is to be connected to, in order to ensure a positive fixation. Leads must be specially made in fixed lengths with the fittings attached. Since human bodies are of various sizes, this results in the necessity of stocking many different lengths of leads which is expensive and impractical, or the implanting of leads that are longer than necessary and the coiling of the excess length within the body. The excess length adds further bulk to the implanted material and provides additional opportunities for failure and trauma due to the presence and flexing of the superfluous lead length.
In certain situations in the art of implantable medical products it is necessary to connect two leads together, or as the terminology has developed in the art, to connect a "receiver extension" or an "extension" to a lead. This situation arises in the art of implanting stimulators to control pain as a result of the fact that whether or not pain can be successfully treated with this method varies from person to person and is dependent upon the site of stimulation and other feature. Thus, the typical procedure for such treatment is as follows: a small incision is made in the region of the site to be stimulated and a lead is inserted and the electrode placed at the stimulation site; stimulation is provided for a trial period which may last a number of days; if stimulation at the site is successful enough in controlling pain to warrant the implantation of a device, a receiver for receiving stimulation signal or a pulse generator for producing stimulation signals is then implanted in the body of the patient. Generally the receiver or pulse generator is placed in a location in the body which is comfortable, safe and cosmetically satisfactory, which location generally is away from the site of stimulation. Further, it is highly desirable to leave the originally implanted lead in place, since its effectiveness has been proven and it would be traumatic to remove it. Thus, a receiver extension or an extension is provided that extends from the point of implant of the receiver or pulse generator to the site of the original incision where it is connected to the original lead. Because of the variability in placement of the receiver or pulse generator and the variability in the placement of the stimulating electrode and because of the other factors peculiar to implantable devices discussed above, it is highly desirable to have a lead connector which is small in size, yet provides reliable positive fixation and, at the same time, provides for connection to both the extension and lead at any point along their length without the use of special adaptors.